In recent years, a so-called contactless IC card has become popular as a ticket for a train and a prepaid card, taking advantages of user-friendliness for a user, excellent durability, concurrent accessibility to a plurality of cards, ease of maintenance, etc.
In a case where these contactless IC cards approach a dedicated reader/writer (contactless IC card reader/writer) connected to a network, the reader/writer performs writing, erasing, updating, etc. of data stored inside.
Further, recently it has been considered to provide a function of the contactless IC card in a mobile phone terminal which is an example of the mobile wireless communication terminal, and it is thought that new services, such as electronic banking etc. may be offered by providing the mobile phone terminal with the contactless IC card Function.
Furthermore, Japanese Patent Application Publication (KOKAI/No. H11-213111 proposes to provide the mobile phone terminal with the contactless IC card reader/writer.
Incidentally, since the contactless IC card is supplied with energy by an alternating magnetic field of carrier waves which is generated by a reader/writer, such as 13.56 MHz etc., a nonlinear element, such as a diode is connected to an antenna for the IC card. Thus, in the case where the nonlinear element is connected to the antenna for IC card, if communications are performed between the contactless IC card and the reader/writer, high order harmonics in the carrier waves, such as 13.56 MHz etc., may take place.
Further, a communication distance of a proximity-type contactless IC card is a very short distance, as short as approximately 10 cm. Thus, in a case where a mobile phone terminal is provided with a contactless IC card reader/writer and a contactless IC card communicates with the reader/writer provided for the mobile phone terminal, the high order harmonics of the carrier wave generated by the reader/writer, and a mixture wave (spurious radiation wave) of the high order harmonics of the carrier wave and a mobile-phone terminal transmission wave may become disturbance waves in a reception bandwidth of the mobile phone terminal. As a result, there is a problem that receiving performances of the mobile phone terminal may deteriorate.
Especially, in the case where the contactless IC card reader/writer is provided for the mobile phone terminal, it is conceivable that the mobile phone terminal may be used as means for communicating with a server which manages fee charging information etc. when writing the fee charging information etc. into an external contactless card. For this reason, communication quality of the mobile phone terminal at the time of using the contactless IC card reader/writer function is required to be of high quality.
As examples In which the disturbance wave is generated in a reception band of a mobile phone terminal, a mobile phone system in a W-CDMA (Wideband-Code Division Multiple Access) system currently used in Japan and a mobile phone system of a cdma2000 system will be described typically hereafter. In addition, these two systems use a full-duplex system in which transmission and reception are simultaneously carried out, and they have a mechanism for generating the disturbance wave in the reception band even if any radio channel is selected at the time of communications.
Firstly a mobile phone system of the W-CDMA system will be described.
The mobile phone system of the W-CDMA system is a system in which a base station transmission frequency (or, mobile phone terminal reception frequency) is 2130 MHz-2170 MHz, a mobile-phone terminal transmission frequency (or, base station reception frequency) is 1940 MHz-1980 MHz, a transmission/reception frequency interval is 190 MHz, and a bandwidth is 3.84 MHz. The transmission and reception are fundamentally in full-duplex.
The mobile-phone terminal reception frequency and the mobile-phone terminal transmission frequency can be expressed by the following equation (1). In addition, in equation (1), Fwdc represents a mobile-phone terminal reception career frequency, and Fwtc represents a mobile-home terminal transmission career frequency.Fwdc=Fwtc+190 MHz   (1)
In a case where the mobile-phone terminal transmission wave is inputted into the contactless IC card reader/writer, a contactless IC card reader/writer transmission wave and the mobile-phone terminal transmission wave are mixed due to nonlinear characteristics of a circuit element provided for the contactless IC card reader/writer. As a result, a spurious radiation wave is generated in a frequency range of the following equation (2). In addition, in equation (2), Ficn represents a spurious radiation-wave frequency range of the contactless IC card reader/writer, Fwtc represents a mobile-phone terminal transmission career frequency, Fwtd represents a mobile-phone terminal transmission frequency width, Fict represents a contactless IC card reader/writer transmission frequency, and p is a positive integer.Ficn=Fwtc±Fwtd/2±Fict×p   (2)
Further, in view of a case where the contactless IC card reader/writer transmission frequency is 13.56 MHz and further p of equation (2) is 14, the spurious radiation-wave frequency range Ficn of the contactless IC card reader/writer is expressed by the following equation (3).
                                                        Ficn              =                                                Fwtc                  ±                                      1.92                    ⁢                                                                                  ⁢                    MHz                                                  +                                  13.56                  ⁢                                                                          ⁢                  MHz                  ×                  14                                                                                                        =                              Fwtc                +                                                      189.84                    ⁢                                                                                  ⁢                    MHz                                    ±                                      1.92                    ⁢                                                                                  ⁢                    MHz                                                                                                          (        3        )            
where, the spurious radiation wave of the contactless IC card reader/writer expressed by this equation (3) is close to the reception career frequency of the mobile phone terminal of the W-CDMA system as explained with regard to equation (1). Further, in considering that the mobile-phone terminal reception bandwidth of the W-CDMA system is 3.84 MHz, the spurious radiation wave of the contactless IC card reader/writer falls within the reception band of the mobile phone terminal of the W-CDMA system. In other words, assuming that the transmission frequency of the mobile phone terminal of the W-CDMA system is 1940 MHz, for example, as shown in FIG. 13 he fourteenth order harmonic of the carrier wave of the contactless IC card reader/writer generates noise in a band of 1940 MHz±1.92 MHz+14*13.56 MHz=2129.84±1.92 MHz 2127.92 MHz to 2131.76 MHz). This noise component falls within a reception band of 2130 MHz±1.92 MHz of the mobile-phone terminal reception frequency.
Therefore, in a case where the mobile phone terminal of the W-CDMA system carries out transmission when transmission is performed by the contactless IC card reader/writer and, reception sensitivity of the mobile phone terminal is degraded in every radio channel and a call may be disconnected in the worst case.
Next, the case of the mobile phone system of the cdma2000 system will be described.
The mobile phone system of the cdma2000 system is a system in which the base station transmission frequency (or, mobile-phone terminal reception frequency) is 832 MHz-870 MHz, the mobile phone terminal transmission frequency (or, base station reception frequency) is 887 MHz-925 MHz, the transmission/reception frequency interval is 55 MHz, and the bandwidth is 1.23 MHz. The transmission and reception are fundamentally in full-duplex.
The mobile-phone reception frequency and the mobile-phone transmission frequency can be expressed by the following equation (4). In addition, in equation (4), Fcdc represents a mobile-phone reception career frequency, and Fctc represents a mobile-phone transmission career frequency.Fcdc=Fctc−55 MHz   (4)
In this cdma2000 system, in a case where the mobile-phone terminal transmission wave is inputted into the contactless IC card reader/writer, the contactless IC card reader/writer transmission wave and the mobile-phone terminal transmission wave are mixed due to the nonlinear characteristics of the circuit element of the contactless IC card reader/writer. As a result, the spurious radiation wave is generated in a frequency range of the following equation (5). It is noted that, in equation (5), Ficn represents a spurious radiation-wave frequency range of the contactless IC card reader/writer, Fctc represents a mobile-phone terminal transmission career frequency, Fctd represents a mobile-phone terminal transmission frequency width, Fict represents a contactless IC card reader/writer transmission frequency, and p is a positive integer.Ficn=Fctc±Fctd/2±Fict×p   (5)
Further, in view of a case where the contactless IC card reader/writer transmission frequency is 13.56 MHz and further p of equation (5) is 4, the spurious radiation-wave frequency range Ficn of the contactless IC card reader/writer is expressed by the following equation (6).
                                                        Ficn              =                                                Fctc                  ±                                      0.615                    ⁢                                                                                  ⁢                    MHz                                                  -                                  13.56                  ⁢                                                                          ⁢                  MHz                  ×                  4                                                                                                        =                              Fctc                -                                                      54.24                    ⁢                                                                                  ⁢                    MHz                                    ±                                      0.615                    ⁢                                                                                  ⁢                    MHz                                                                                                          (        6        )            
where, the spurious radiation wave of the contactless IC card reader/writer expressed by this equation (6) is close to the reception career frequency of the mobile phone terminal of the cdma2000 system as explained with regard to equation (4). Furthers when considering that the mobile-phone terminal reception bandwidth of the cdma2000 system is 1.23 MHz, the spurious radiation wave of the contactless IC card reader/writer falls within the reception band of the mobile phone terminal of the cdma2000 system. In other words, assuming that the transmission frequency of the mobile phone terminal of the cdma2000 system is 898 MHz, for example, as shown in FIG. 14 the fourth order harmonic of the carrier wave of the contactless IC card reader/writer generates noise in a band of 989 MHz±0.615 MHz−4* 13.56 MHz=843.76±0.615 MHz (843.14 MHz-844.38 MHz) band. This noise component fails within a reception band of 843 MHz±0.615 MHz of the mobile-phone terminal reception frequency.
Therefore, in a case where the mobile phone terminal of the cdma2000 system carries out the transmission when the transmission is performed by the contactless IC card reader/writer, the reception sensitivity of the mobile phone terminal is degraded in every radio channel and the call may be disconnected in the worst case.
The present invention is proposed in view of such conditions, and aims to provide, in a case where a mobile wireless communication terminal provided with a contactless IC card reader/writer function or a contactless IC card function, the mobile wireless communication terminal capable of ameliorating degradation in reception sensitivity at the time of the wireless communications produced by the spurious radiation wave generated from the contactless IC card reader/writer and its mobile wireless communication system.